pdfsandwich generates "sandwich" OCR pdf files, i.e. pdf files which contain
only images (no text) will be processed by optical character recognition (OCR)
and the text will be added to each page invisibly "behind" the images.

pdfsandwich is a command line tool which is supposed to be useful to OCR
scanned books or journals. It is able to recognize the page layout even for
multicolumn text.
